This invention relates to surface functionalized silicon substrates. More particularly, this invention is directed to silicon surfaces having covalently bound monolayers formed by an electrochemically-induced reaction between silicon hydride moieties on the silicon surface and optionally substituted alkynes.
Silicon surface chemistry is of fundamental technical significance because of the ubiquitous role of silicon in modem technology; yet silicon/organic chemistry is only just beginning to be investigated. Virtually all microprocessor chips in electronic products are based upon crystalline silicon wafers. Control of silicon surface chemistry is crucial to allow access to technologically functional thin films for fabrication of new electronic devices. In 1990, Canham and co-workers showed that silicon wafers could be etched using hydrofluoric acid to produce a porous layer that is only a few microns thick (termed porous silicon) and exhibits photoluminescence upon exposure to UV light (Canham, L. T. AppL. Phys. Lett. 1990, 57, 1046). The surface of porous silicon (Si) is populated with metastable Sixe2x80x94Hx bonds (x=1,2,3), exposed Sixe2x80x94Si bonds, and defects such as open valence, xe2x80x9cdanglingxe2x80x9d Si atoms. Potential applications for porous silicon include uses as chemical sensors, biosensors, optoelectronic devices such as electroluminescent displays, photodetectors, mass spectrometry (desorption ionization on silicon or DIOS), interfacing with neurons and other nerve cells, and as a matrix for photopumped tunable lasers. As a result, modification and characterization of photoluminescent porous silicon surfaces has become an area of intense interest.
Recent developments in the functionalization of porous silicon have enabled Sixe2x80x94C bonds to be formed on the porousxe2x80x94Si surface by attacking the weak Sixe2x80x94Si bonds of exposed nanocrystalline submaterial with Grignard or alkyllithium reagents. Grignard and alkyllithium transmetallation and the use of Lewis acid catalysis have also been used to exploit the great population of surface Sixe2x80x94H bonds. Thermal, radical-mediated, and UV photolytic alkene hydrosilylation has also been reported for flat Si and Si hydride surfaces. In general, chemistry that works on porous silicon also applies to flat Si (100) and Si (111) surfaces based on substantial literature precedent. Additionally, using the Si surface as a semiconducting electrode, several workers have recently reported electrochemical Sixe2x80x94C bond formation by direct grafting, an approach with few parallels to soluble, molecular silane chemistry.
The present invention is directed to a new method of functionalizing the Si surfaces by electrochemically grafting terminal alkynes to silicon resulting in two distinct surface derivations depending on the polarity of the surface bias. Cathodic electrografting (CEG) directly attaches alkynes to the surface, whereas anodic electrografting (AEG) of alkynes yields an alkyl surface.